1. Technical Field
This invention relates to air laying forming stations and, more particularly, to air laying forming stations for producing nonwoven materials from first and second materials having a difference in characteristic or composition and including a baffle member for directing the flow of the second material by gravity and independently of the first material.
2. Discussion
Conventional air laying forming stations (ALFS) use one air stream to transport and distribute blends of materials which are different in characteristic or composition, for example high absorbency materials (HAM) and fibrous materials (FM). As differences between the materials (such as size, shape, and density) increase, the materials behave differently in the common air stream and undesirable and uncontrollable separation of the blend occurs. Separation problems increase as the flow distance increases and as the width of the ALFS and the nonwoven material increase in the cross machine direction (CD). Such increasing distances, widths and behavioral differences of the materials in the air stream result in highly variable basis weights in the machine direction (MD) and the CD. Conventional ALFS have typically been unable to provide uniform and controlled distribution of HAM in nonwoven materials, especially as CD widths approach and exceed 1 meter. Additionally, conventional ALFS have been unable to uniformly and controllably distribute HAM in nonwoven materials as mass concentrations of HAM approach and exceed 15-20% by weight.
As a result of transporting the blend of materials in a single air stream, the conventional ALFS generally produce only nearly homogenous blends of HAM and FM and cannot produce nonwoven materials having multiple zones of HAM and FM concentrations in the Z-axis (orthogonal to the MD and CD). Thus, a single conventional ALFS cannot produce a nonwoven material with nearly HAM-free or reduced-HAM dusting zones in order to better contain the HAM within the nonwoven material during further processing and consumer use. Benefits of providing multiple HAM concentration zones along the Z-axis are well recognized within the art for various applications, including diapers, feminine hygiene products, etc. The art generally focuses on two key benefits of variable HAM concentration zones. The first is an improvement to HAM efficiency and effectiveness, and the second is improved containment of HAM within the structure.
Transporting the HAM and FM to form absorbent bodies using separate air streams has been proposed, for example in U.S. Pat. No. 4,927,582 to Bryson. In Bryson, blower 48 propels HAM 28 via one or more pipeline conduits 20 into forming chamber 10. Vacuum source 32 creates an air flow, indicated by arrows 36, which draws FM 14 against forming screen 30. Baffles 34 are attached to opposing sidewalls (e.g. in a CD) and are used to regulate the cross-directional distribution of HAM across web 41.
In use, however, air injection to propel HAM 28 into forming chamber 10 disrupts the flow of FM 14 onto forming screen 30 adversely affecting uniform distribution of FM 14. Use of one or more pipeline conduits 20 provides poor CD control of the basis weight of HAM 28 deposited onto forming screen 30, particularly for wide machines (in the CD). In addition, the use and positioning of baffles 34 disrupts FM 14 formation on forming screen 30.
In Bryson, HAM and FM are introduced separately, however CD basis weight profiling of HAM 28 is accomplished after HAM 28 mixes with FM 14 using baffles 34. Profiling HAM 28 using baffles 34 as disclosed in Bryson also changes the CD basis weight profile of FM 14. Thus, independent CD basis weight profiling of FM 14 and HAM 28 is not achieved.
Therefore, an ALFS which forms a nonwoven material with reduced MD and CD variability of a second material, (for example HAM) within a first material (for example FM) which has a significant difference in characteristic or composition is desirable. Additionally, an ALFS which forms a nonwoven material by providing control of the Z-axis placement of a second material (for example HAM) within a first material (for example FM) which has a significant difference in characteristic or composition is desirable.